ARTICLE
Auteur(s) : Zoubida
Charrouf1, Hicham Harhar1, Saïd
Gharby1,2, Dominique Guillaume3
1Laboratoire de chimie des plantes et synthèse
organique et bioorganique, Département de Chimie, Faculté des
Sciences, Université Mohammed V-Agdal, BP 1014, Rabat, Maroc
2Laboratoire Contrôle Qualité, Lesieur-Cristal, 1, Rue
Caporal Corbi, 20300 Roches Noires, Casablanca, Maroc
3CNRS-UMR 6229, Chime thérapeutique, 51 rue Cognacq-Jay,
51100 Reims, France
The argan tree (Argania spinosa (L.) Skeels, sapotaceae) is
endemically growing only in Southwestern Morocco. The area covered
by the argan forest, also named the argan grove, has the shape of
an isosceles triangle, the base of which being along the Atlantic
Ocean and its third summit being 100 km away, east from the
coast. The argan grove has a superficy of 800,000 ha and is in
a region where the association of subtropical temperatures and
oceanic moisture creates a unique ecosystem that was recognized by
the UNESCO as a biosphere reserve in 1998. The argan tree is
particularly well adapted for this kind of environment since its
deep rooting system allows the survival of the tree on poor and dry
soils while limiting erosion and desertification. Over the years,
an agroforestry system based on the argan tree has prospered. The
tree was providing its wood as fuel and for construction, its
leaves as forage, its shadow for protecting family-scale culture,
and its fruits to prepare argan oil. However, nowadays this
forestry system is no longer at equilibrium and the argan grove is
severely endangered. Its supercify is constantly shrinking and the
tree density is permanently decreasing. This is due to the
unfortunate combination of multiple factors including several
consecutive extremely arid years, lack of care and
over-exploitation of the trees by the local population, lack of
long-term management of the argan forest by the administrative
autorities until the 1980s, and the culture of water-gobbling
vegetable mainly to satisfy the need of the fast-booming tourist
industry. To inverse this dramatic trend and rescue the argan grove
as well as its population, and ultimately stop the desert
progression in Southwestern Morocco, a nation-wide program has been
initiated in Morocco in the late 1980s. This program was based on
the assumption that only an increase in the argan tree monetary
value could save the argan forest, and that the local population
would actively adhere to this program only if they were directly
benefiting of a major part of the expected financial outputs. The
next pages describe the main achievements of this program and the
work that still needs to be done before its final completion.
What could enhance the argan tree value?
Argan tree secondary metabolites
The discovery of new marketable argan tree derivatives or of new
market niches was a prerequisite to justify the domestication of
the tree and its reimplantation on large areas. To have a chance of
enhancing the argan tree value, it was necessary either to identify
new outputs possibly different from those traditionally known or to
strongly improve the commercial value of the known ones. Both ways
have been explored for fifteen years and are still currently
explored. The systematic phytochemical analysis of all argan tree
parts was undertaken to identify new secondary metabolites possibly
allowing the development of new outputs. Because all members of the
sapotaceae family contain a high level of saponins and because
saponins possess numerous biological activities [1], this class of
compounds was the first to be investigated. Indeed, the presence of
high levels of saponins belonging to the Δ-12 oleanane subgroup was
rapidly confirmed. Succesive studies allowed the identification of
new saponins: five from the argan kernels [2], eight from its trunk
[3, 4], two from its seed shell [5], one from its seed pulp [6] in
addition to several already known saponins [7]. Although most of
these saponins display antiinflammatory and antifungus properties,
their biological activity is not efficient enough to justify
further developments in this field. More interestingly, one of the
argan saponins, named arganine C, has shown strong inhibitory
properties against HIV entry into cells in a cell fusion assay [8]
and a mixture of argan saponins has been shown to possess lipolytic
activating properties on human adipocytes as well as DNA protective
effects against UV-B [7, 9]. Such results could lead to the
development of argan secondary metabolites in the highly lucrative
drug or cosmetic fields. However, though highly promising, these
results are too preliminary to ascertain the economic future of the
argan grove on the short term. Consequently, other metabolites are
currently also actively explored to enhance argan tree value.
Flavonoids constitute the second class of argan metabolites
currently actively investigated and considered as able to provide a
direct access to a viable market. The recent discovery of the
anti-collagenase activity of the crude flavonoid fraction of argan
leaves has led to envisage their introduction in cosmetic
preparations [10]. However, as mentionned for the saponins, the
possibility of sustainable incomes from an industrial use of argan
leaves remains remote and uncertain.
Improvement of traditionally known uses of argan derivatives is
therefore a method that should not be neglected to ensure the argan
grove preservation.
Argan oil
Argan oil has been traditionally used by the argan forest dwellers
for centuries [11]. It is prepared by pressing argan fruit kernels.
When carried out on a family scale, argan oil preparation is
exclusively performed by women. Recent improvements that do not
alter the oil physico-chemical properties [12] have been brought to
the oil preparative process and, to respect the tradition,
implemented in women rural cooperatives. Both extraction methods
have already been described in full details [13, 14]. Even though
some amount of mechanization has been introduced for some the
preparative steps, the full process remains slow and requires the
collect of huge quanties of kernels. This explains the elevated
price of the oil.
Two kinds of argan oil can be found on the market: the cosmetic
or edible argan oil. Both oils are virgin (cold-press) oils but
cosmetic grade argan oil is prepared from non-roasted argan kernels
whereas edible argan oil is prepared by pressing slightly roasted
kernels. This step dramatically modifies the taste of the edible
oil and is responsible for its unique hazelnut taste and flavor.
Chemical investigation of the odorants contained in edible and
cosmetic argan oil has evidenced composition differences even
though the odorant(s) responsible for the hazelnut flavor has(ve)
not been identified yet [15].
Argan oil density at 20°C is between 0.906 to 0.919; its
refractive index is 1.463-1.472. Extra virgin argan oil has an acid
value lower than 0.8 [16]. Glycerides, including 95% of
triglycerides, constitute 99% of argan oil. The main fatty acids in
argan oil are oleic acid (46-48%), linoleic acid (31-35%), palmitic
acid (11-14%), and stearic acid (4-7%) [9, 17]. Because argan oil
is not refined, it still contains 1% of unsaponifiable matters.
They include carotenes (37%), tocopherols (8%), triterpene alcohols
(20%), sterols (29%), and xantophyls (5%). Tocopherol level is
between 600 and 900 mg/kg. The main tocopherol found in argan
oil is γ-tocopherol (between 81 and 92%) [18], it is a strong
anti-oxidative agent. α-, β-, and δ-tocopherols represent 2.4 to
6.5%, 0.1 to 0.3%, and 6.2 to 12.8%, respectively, of the total
tocopherol fraction. The simultaneous presence of high levels of
unsaturated fatty acids, γ-tocopherol, and sterols is currently
believed to be the reason for the hypocholesterolemiant, hepato and
cardioprotective properties of argan oil [19, 20]. These compounds
could also provide a cancer chemoprotective effect [21].
Research on argan oil currently in progress
The main concerns currently addressed to argan oil are 1) the
certification of its purity and 2) its preservation. The elevated
price of argan oil makes it particularly prone to adulteration. A
simple fatty acid analysis is not sufficient to certify the argan
oil authenticity since several vegetable oils have a sufficiently
close composition so it could be possible to obtain a similar
composition by mixing cheap oils in calculated amounts. It has
recently ben shown that campesterol, a sterol common in all
ordinary vegetable oils, is lacking in argan oil composition. Since
campesterol can be easily detected by gas-chromatography analysis,
a method taking advantage of the lack of campesterol has been
recently proposed, together with a fatty acid composition analysis,
to detect argan oil adulteration [22].
Because of its high content in tocopherols and phenols, two
families of antioxidant derivatives, argan oil preservation time
can be expected to be long. The short preservation time observed
for the traditionally prepared oil is directly related to the
addition of water during the extraction procedure. Water-addition
being suppressed in the rural women cooperatives, argan oil
preservation ability is now strongly improved. Nevertheless
cosmetic and edible argan oils have a quite different preservation
time, the shelf life of edible argan oil being twice longer than
that of the cosmetic oil. The oil peroxide index can be used to
monitor the oil preservation ability. Comparison of the peroxide
index of cosmetic vs edible argan oil samples stored at 25 °C
in brown-colored or clear glass under inert atmosphere have
demonstrated that whereas freshly prepared edible and cosmetic
argan oil samples have similar peroxide index, after three months,
the peroxide index of cosmetic oil is threefold (dark glass) to
fourfold (clear glass) higher than that of edible argan oil after
the same amount of time. This clearly shows that the sunlight has
some incidence on the peroxide index (preservation time) and
sugggests that an additional factor intrinsec to the oil is
responsible for the difference in preservation time. The hypothesis
of the formation of derivatives having high preservative properties
or of the destruction of strongly but still unknown oxidative
agents during the roasting step is currently investigated, as well
as other hypotheses.
Conclusion
On the short-term, the future of the argan grove appears to be
secured by the economic success of argan oil. However linking the
argan grove preservation to a single produce, whatever its quality
can be, is highly dangerous. Efforts are currently performed in
Morooco to certify the oil quality, and consequently ascertain
consumer fidelity. The recently obtained Geographic Indication of
argan oil is also a positive factor that is likely to satisfy the
consumers. However, on a long-term standpoint, it is still
necessary to identify new derivatives allowing the enhancement of
the argan tree value and hence avoid fluctuations on the oil market
that, as it is now, could be fatale in case of consumer
disaffection. For the moment, leaf flavonoids appear to be the best
candidates to ensure this function.
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